Overview

Material level is an important parameter in industrial production. There are many methods for measuring material levels, and different level gauges with different measurement principles can be used for different working conditions and media. Several commonly used level measuring instruments, such as air blowing, static pressure, floating ball, heavy hammer, ultrasonic, etc., have their own characteristics and application ranges.

The radar level gauge utilizes advanced radar measurement technology and plays an increasingly important role in industrial production due to its excellent performance, especially under harsh measurement conditions such as stirring, high temperature, large steam, strong corrosiveness of the medium, and easy scarring in tanks.

Principle and Technical Performance

Radar waves are a special form of electromagnetic waves, and radar level gauges utilize the unique properties of electromagnetic waves for level detection. The physical properties of electromagnetic waves are similar to visible light, and their propagation speed is equivalent to the speed of light.

Its frequency is300MHz-3000GHzElectromagnetic waves can penetrate interference sources such as space vapor and dust, and are easily reflected when encountering obstacles. The better the conductivity or dielectric constant of the measured medium, the better the reflection effect of the echo signal.

The higher the frequency of the radar wave, the smaller the emission angle, the greater the energy (magnetic flux or field strength) per unit area, and the smaller the attenuation of the wave, the better the measurement effect of the radar level gauge.

1Basic principles of radar level gauge

The radar level gauge consists of several parts, including a transmitting and receiving device, a signal processor, an antenna, an operation panel, a display, and a fault alarm.

The basic principle of radar level gauges is transmission reflection reception. The antenna of the radar sensor emits the minimum in the form of a beam5.8GHzThe radar signal. The reflected signal is still received by the antenna, and the running time of the radar pulse signal from transmission to reception is proportional to the distance from the sensor to the surface of the medium and the level of the object. Namely:h= H–vt/2in the formulahFor material level;HFor slot height;vFor radar wave velocity;tThe interval time between the transmission and reception of radar waves.

2Advanced technology for measuring material levels using radar level gauges:

(1)Application of New Echo Processing Technology

From the measurement principle of radar level gauge, it can be known that radar level gauge measures the level by processing the time when radar waves are emitted from the probe to the surface of the medium and then returned to the probe. There are many interference signals mixed in the reflected signal. Therefore, the processing of real echoes and the identification technology of various false echoes have become the key factors for radar level gauge to accurately measure.

(2)Measurement data processing:

Due to factors such as liquid level fluctuations and random noise, a large amount of noise is inevitably mixed in the detection signal. In order to improve the accuracy of detection, it is necessary to process the detection signal and eliminate noise as much as possible. After extensive experimental verification, the use of data smoothing methods can achieve satisfactory results. This method can also effectively overcome the influence of the agitator inside the tank on measurement.

(3)Characteristics of radar level gauge:

Due to the use of advanced echo processing and data processing techniques, as well as the high frequency and good penetration performance of radar waves, radar level gauges have better performance than contact level gauges and similar non-contact level gauges.

① Can measure continuously and accurately under harsh conditions.

② Easy to operate and convenient to debug.

③ Accurate, safe, and energy-efficient.

④ No maintenance required and highly reliable.

⑤ Almost all media can be measured.

Issues to be noted during installation

(1)When measuring liquid materials, the axis of the sensor is kept perpendicular to the surface of the medium; When measuring solid materials, the sensor needs to be tilted at a certain angle due to the stacking angle of the solid medium.

(2)Try to avoid devices that cause false reflections within the emission angle. Especially avoid being located closest to the antenna1/3There are obstacle devices in the conical emission area (because the closer the obstacle device is, the stronger the false reflection signal). If it is unavoidable, it is recommended to use a refractive plate to refract the excessively strong false reflection signal away. This can reduce the energy density of false echoes, making it easier for the sensor to filter out false signals.

(3)Avoid the feeding port to prevent false reflections.

(4)The sensor should not be installed at the center of the arched tank (otherwise the false echo received by the sensor will be enhanced), nor should it be installed very close to the tank wall. The best installation position is within the radius of the container1/2Here.

(5)Avoid installing in areas with strong eddy currents. For example, due to stirring or strong chemical reactions, it is recommended to use a waveguide or bypass tube for measurement.

(6)If the sensor is installed on the connector, the antenna must protrude from the connector. The horn shaped antenna extends at least through the connecting pipe10mmThe maximum length of the rod antenna connector is100or250mmMinimum takeover diameter250mmThe method of increasing the diameter of the connecting pipe can be adopted to reduce the interference echo caused by the connecting pipe.

(7)Regarding waveguide antenna: The inner wall of the waveguide must be smooth, and the waveguide with an opening below must reach the required low liquid level in order to measure in the pipeline. The type plate of the sensor should be aligned with the axis of the waveguide opening. If the measured dielectric constant is less than4It is necessary to install a reflector at the end of the waveguide or bend the end of the waveguide to a certain degree to refract the reflected echoes from the bottom of the container.

Problems and Solutions in Applications

The radar level gauge used in some working conditions has encountered some problems due to improper sensor installation positions and conditions. Below are some solutions to the problems encountered during use,For everyone's reference.

1．Solution to probe scarring and frequent malfunctions

The first method is to raise the installation position of the probe, but sometimes the installation conditions are limited and cannot be raised. In this case, the method of interlocking the material level measurement value with the pump of the tank should be adopted to solve this problem: reduce the highest material level setting value0.5mWhen the material level reaches the highest value, the feed pump can be stopped or the discharge pump can be turned on.

2．Improvement Measures for Radar Level Gauge Submerged

The solution to this problem is to replace the radar level gauge with a waveguide type measurement. Still installing the waveguide radar level gauge at the original opening, with the waveguide higher than the exhaust pipe0.2mIn this way, even in adverse conditions where slurry overflows from the exhaust pipe, the antenna of the level gauge will not be submerged by the slurry, and interference from the vortex of the agitator and a large amount of steam escaping from the probe are avoided, reducing damage to the probe. At the same time, due to the good focusing effect of the waveguide, the received radar wave signal is stronger, achieving good measurement results. The use of waveguide measurement method can improve the measurement conditions of the meter and enhance the measurement performance of the instrument,Has high promotion and application value.

3．Influence of foam on measurement

Dry foam and wet foam can reflect back the radar wave and have no impact on the measurement; The neutral foam will absorb and diffuse the radar wave, thus seriously affecting the reflection of the echo or even no echo. When the medium surface is thick and thick foam, the measurement error is large or cannot be measured. Under this condition, the radar level meter has no advantage, which is the limitation of its application.

4．For the treatment of antenna scars

Materials with low dielectric constant have no effect on the measurement in a dry state, while materials with high dielectric constant have an impact on the measurement. Compressed air can be used for blowing (or rinsing with clean water), and the cooled compressed air can lower the temperature of flanges and electrical components. Acidic cleaning solution can also be used to clean alkaline scars, but material level measurement cannot be performed during the cleaning period.

Xi'an Dinghua Electronics Co., Ltd，1992Established in, currently located in Xi'an, Shaanxi Province, it is a high-tech enterprise integrating research and development, production, sales, and engineering services of radar level instruments. At present, the company has a series of products including radar level gauges, external liquid level instruments, tuning fork level switches, electro-hydraulic actuators, ultrasonic flow meters, external thermometers, etc., all of which have undergone multiple complex working conditions tests on site and are widely used in industries such as petroleum, chemical, power, coal, metallurgy, food, and medicine. Professional selection guidance, excellent product quality, reasonable product prices, convenient supply cycles, and comprehensivePre sales, in sales, and after-sales services